The motivation for this project is to learn how antigen receptors on lymphocytes function in regulating cellular differentiation. We will examine the behavior of antigen reactive cells under various conditions in vitro and in adoptive transfer system. Receptor-antigen interactions on cell surfaces will be studied by fluorescence and electron microscopy. We will compare the biological and physical properties of specific antigen binding cells isolated before immunization at various stages in an immune response. At the same time, we intend to continue affinity labeling studies to compare common and variable structural features of the active sites of homogeneous antipolysaccharide antibodies. BIBLIOGRAPHIC REFERENCES: Cammisuli, Salvatore, and Leon Wofsy, Hapten-sandwich labeling III. Bifunctional reagents for immunospecific labeling of cell surface antigens. J. Immunol. 117, 1695 (1976).